1. Field of the Invention
The present invention concerns a support structure for a power station having a prestressed cylindrical pressure vessel. The pressure vessel is preferably of reinforced concrete. More particularly, the support structure comprises an annular ring of supports on a foundation in a specific arrangement.
2. Background of the Prior Art
Large size pressure vessels are being built in particular to house components of nuclear power stations. They consist of a pressure bearing external shell of reinforced concrete. Inside the shell, a cavity and a liner for the sealing of said cavity are found. Such pressure vessels pose problems in relation to their supporting structure. The supporting foundation must be safe with respect to shifting during earthquakes. Deformations of the concrete body due to creep and thermal stresses during operation and in the case of failure events must be absorbed. The foundations must also absorb shifting, resulting from the stresses normally encountered during operation of a nuclear reactor as well as the hypothetical stress for the reactor design.
There are known arrangements for the support of reactor pressure vessels that are capable of absorbing the radial forces generated by the thermal expansion of the pressure vessel. For example in West German Published Application No. 2 432 011 an arrangement for the thermally mobile supporting of a reactor pressure vessel is described. The pressure vessel is fastened to the holding members of a bursting shield by means of bending springs. The bursting shield surrounds the pressure vessel at a distance. The exposure to high axial deformation forces of the reactor pressure vessel is made possible within the bursting safeguard. At the same time, the limited, radial, centering support of the pressure vessel on the holding members of the supporting structure is assured. The reactor pressure vessel is, therefore, supported by means of bending springs which are attached on one end to the holding members and at the other end with the supporting members of the reactor pressure vessel such that the bending springs are stressed in tension by the axial load of the reactor pressure vessel and by its radial thermal expansion. The bending of the spring, therefore, requires that a gap be provided surrounding the reactor pressure vessel.
A further arrangement disclosed in West German Offenlegungsschrift No. 2 021 031 enables the prevention of damage by earthquakes to buildings. This arrangement has supporting bearings which consist of rocker bodies and roller plates to hold the rocker bodies. The accelerating and impact forces of an earthquake are reduced through this arrangement to magnitudes that are acceptable in terms of damage to buildings. During vibrations of the ground, movements of the foundation in the horizontal direction are resolved into vertical and horizontal components of motion by means of the rocker bodies, and the acceleration forces in the vertical direction are reduced by oscillating positions. This is achieved mainly by providing the supporting bodies with two spherical surfaces having radii larger than one-half of the height of the supporting body. In addition, the supporting body with the ascendant resting on it forms a system capable of oscillating. The disadvantage of this system is that an unsecured deflection exists in the case of maximum vibrations. Another disadvantage is the single point force application of the rocker body on the bearing shells.
A further known supporting structure for a nuclear reactor consists of several supports arranged on a solid bottom plate. A supporting jacket is placed upon these supports with the insertion of rollers and the like. This supporting structure is represented in West German Published Application No. 1 559 153. The annular body and the height of the supports permit an undefined width of swaying of the system. In the case of maximum swaying, the danger of the buckling of the annular body at a point of stress is not precluded.